This invention relates to the opening of a gap for the passage of the needle thread between the nonrotating bobbin case of a rotary sewing machine loop taker and the rotation restraining means for the bobbin thread case. The gap between the position finger and the bobbin case, through which the thread has to pass just prior to stitch setting, tends to be closed due to the frictional forces caused by the rotating loop taker body during operation. This results in an interference with passage of the thread loop which can cause several sewing malfunctions, for example, the formation of loops in the resulting stitches, imperfect stitch setting, and thread breakage.
It is known in the sewing machine art to provide a bobbin thread case opener for the purpose of allowing the passage of the needle thread between the bobbin thread case and the bobbin case rotation restraining means. Conventional bobbin case opener employs two spaced bobbin case rotation restraining means relatively movable so as to be alternately effective and thus to provide for an escapement. In such conventional bobbin case opener mechanism, the timing of the opener drive is critical, and the spaced rotation restraining means double the chance of a problem arising as the thread passes there through.